Various means and procedures have been developed in recent years to clear or open occluded arteries and other body vessels in order to restore the necessary circulation of blood through the body. In many situations, such intravessel procedures are preferable to "by-pass" operations in which the affected vessel is effectively shunted because intravessel procedures can be relatively quickly performed and do not require an incision into the chest cavity or some other part of the body. Consequently, various procedures and several different devices for performing these procedures have been developed.
In general, there are three ways to eliminate or ameliorate the difficulties caused by an occlusion in an artery. First, it may be possible to dissolve the obstructive tissue causing the occlusion by the ingestion or injection of properly selected medicaments. Such treatment, however, may be ineffective due to an excessive time for response or undesirable due to adverse side effects. Second, well known angioplasty procedures may be used. With the angioplasty procedures, however, the obstructive tissue causing the occlusion remains in situ after the procedure is performed. Thus, the problem may be compromised but it is not eliminated and there remains the real probability there will be a restenosis. Third, atherectomy related procedures may be performed.
In any atherectomy procedure, the obstructive tissue causing the occlusion in the vessel (or at least a part of this obstructive tissue) is cut or clipped from the lumen of the vessel. As should be readily apparent, the instruments used for this purpose require specifically designed cutting devices. Further, the devices which are used for controlling the position of the cutting device in the lumen require special fabrication and design considerations. Specifically, both the cutting device itself and whatever control elements are inserted into the vessel with the cutting device must be miniaturized.
Several atherectomy related devices have been previously disclosed. Exemplary of such devices is Husted U.S. Pat. No. 4,754,755 which discloses a catheter with a cylindrical rotary blade that is used to clear arterial obstructions. As another example of an atherectomy device, Shiber U.S. Pat. No. 4,732,154 discloses a rotary catheter system for this same purpose. For each of the devices disclosed in these references, however, the effective cutting area of the blade of the device is limited. This is so because, in these typical devices, the cutting action of the rotating blade is not capable of extending beyond the periphery of the tubular structure which is used to introduce the blade into the vessel. Consequently, the effective cutting area of the blade is limited by the size of the support structure and this support structure, in turn, is limited to the maximum permissible size of the opening that can be used for an entry site. It often happens, however, that the maximum permissible size of the opening for an entry site is smaller than the cross-sectional area of the vessel lumen at the location where the atherectomy cutter is to be operated. Thus, there is a need for an expandable cutter.
The present invention recognizes the need for an atherectomy cutter which can be expanded, once it is positioned within the lumen of a body vessel, to increase the cutting effectiveness of the device. Further, the present invention recognizes the need for a cutter which can have its cutting action expanded through an infinite variety of diameters between given upper and lower limits while the blades are rotating.
In light of the above, it is an object of the present invention to provide a cutter for an atherectomy device which can be expanded once it is inside the lumen of a body vessel. Another object of the present invention is to provide an atherectomy device which can be adjustably expanded to an infinite variety of settings between upper and lower limits as required to excise obstructive tissue from inside the lumen of a body vessel. Still another object of the present invention is to provide an atherectomy device which can be effectively controlled during the cutting of obstructive tissue from the inside of a body vessel. Yet another object of the present invention is to provide an atherectomy device which is easy to use, relatively easy to manufacture and comparatively cost effective.